https://bugs.freedesktop.org/show_bug.cgi?id=88642
--- Comment #2 from Michel Dänzer michel@daenzer.net --- That kind of artifacts is usually due to whole quad mode not being enabled when it should be. The LLVM patch http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20150119/254035.... fixes it.